The present application is directed to tools that provide for moving a spindle in both advance and retract feed directions and specifically to devices and methods to prevent the spindle from becoming jammed at a home position.
Positive feed tools, such as but not limited to feed drills, are conventionally known for performing operations on workpieces formed of substances such as steel, aluminum, titanium, and composites. Positive feed tools include a tool feed mechanism that feeds a bit into a work piece. Conventional applications for positive feed tools include, among other applications, drilling holes in various parts of aircraft.
A positive feed tool generally includes a motor that is attached to a gear head. The gear head includes a spindle that is rotated and moved in forward and retract directions. In use, the motor drives gears in the gear head that advance the spindle in the forward direction to a desired depth to act on the workpiece. The spindle is then moved in the reverse direction away from the workpiece to a home position. When the spindle reaches the home position, it is desirable that the motor is shut off to minimize air usage and to indicate to the operator that the tool function has been completed.
Previous tools have potential reliability problems which can lead to jamming of the spindle in the home position due to a delay or failure in shutting off the motor. These may cause the spindle to go in to a mechanical lock.
Previous tools have employed various aspects to prevent jamming of the spindle. These aspects have included increasing an over-travel distance of the spindle, and slowing the retract speed of the spindle. However, each of these aspects has their own disadvantages in terms of increasing cycle time, adding more complexity to the drive train design and increasing overall size of the gear head. Further, these aspects still have the potential for the spindle to jam in the home position, especially if the signal to stop the motor fails.